The first time I took acid I had a massive feeling of deja vu. That experience reminded me of the excitement and wonder of childhood. When you are on acid, it's like looking at the world for the first time, not just because the world looks so different, but because LSD can actually bring your mind back to a child-like state (temporarily) allowing you to see the world for the first time, again.
By a "child-like state", I don't mean acid will make you a kid again, but that it can temporarily disable your brain's organization system, allowing sensory information that is normally ignored to make it all the way into your consciousness. This puts your mind in a state that is ripe for rewiring, allowing new ideas, concepts, skills, associations -anything, to be integrated into your perceptual model.
All of the wonder, imagination and creativity that were present in your mind as a child comes flowing back again, uninhibited by your experiences.
This is why you may feel like you're seeing the world for the first time (or like when you were young).
One practical application of this is in learning new skills. Under the influence of LSD, one can actually put their mind temporarily in a state where they are capable of learning as easily as a child. If you are interested in learning more about this, I highly recommend reading
LSD: The Problem Solving Psychedelic.
I have a friend who was brought up in a very rigidly structured environment and as a consequence had difficulty understanding concepts that were totally foreign to him. All of his unconscious anxieties and fears have prevented him from being able to get in touch with himself and express himself. He's very athletic, but he was never that good at frisbee because it wasn't something he did much in his younger days. For a while he struggled to throw the disk with any smoothness. He was very tense and rigid, which really hurt his throw. Even with plenty of practice, he was never as smooth as anyone else, until we tried playing frisbee on acid. With a little bit of instruction and guidance he was able to quickly unlearn all of his bad habits and throw as well as the best thrower in our group.
Acid broke down the mental "block" he had developed and allowed him to actually feel the correct way to throw the disk. Once he felt the correct posture and form, he could understand it and it got imprinted in his mind.
Although this one anecdote doesn't prove anything, it does give one example of how LSD can remove mental barriers. For even better examples, take a look at the link I posted above.